The fundamental steps of processing color light-sensitive materials generally include a color-developing step and a silver-removing step. That is, an exposed silver halide color photographic light-sensitive material is introduced into a color-developing step, wherein the silver halide is reduced with a color-developing agent to produce silver and the oxidized color developing agent in turn reacts with a color former to give a dye image. Subsequently, the color photographic material is introduced into a silver-removing step, wherein silver having been produced in the proceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion-complexing agent usually called a fixing agent. Therefore, only a dye image is formed in the thus processed photographic material. In addition to the above-described two fundamental steps of color development and silver removal, actual development processing involves auxiliary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. For example, there are illustrated a hardening bath for preventing the light-sensitive layer from being excessively softened during photographic processing, a stopping bath for effectively stopping the developing reaction, an image-stabilizing bath for stabilizing the image, and a layer-removing bath for removing the backing layer on the support.
The above-described silver removal may be conducted in two ways: one way uses two steps employing a bleaching bath and a fixing bath; and the other way is more simple and conducted in one step employing a bleach-fixing (or blixing) bath containing both a bleaching agent and a fixing agent for the purpose of accelerating the processing and eliminating work.
Ferricyanide and ferric chloride, which have heretofore been used as bleaching agents, are good bleaching agents due to their large oxidizing power. However, a bleaching solution or bleach-fixing solution containing ferricyanide can release poisonous cyanide by photolysis causing environmental pollution. Accordingly, the waste solution thereof must be made completely harmless in view of environmental pollution. A bleaching solution containing ferric chloride as a bleaching agent is not desirable because materials constituting vessels in which the solution is retained are liable to be corroded due to the extremely low pH and large oxidizing power of the solution. In addition, iron hydroxide is precipitated in an emulsion layer during the water-washing step provided after the bleaching step, resulting in stain formation.
On the other hand, potassium dichromate, quinones, copper salts, etc., which have been used as bleaching agents have weak oxidizing power and are difficult to handle.
In recent years, bleach processing using a ferric ion complex salt (e.g., aminopolycarboxylic acid-ferric ion complex salt, particularly iron (III) ethylenediaminetetraacetate complex salt) as a major component has mainly been employed in processing color photographic light-sensitive materials in view of acceleration and simplification of the bleaching step and the need to prevent environmental pollution.
However, ferric ion complex salts have a comparatively small oxidizing power and, therefore, have insufficient bleaching power. A bleaching or bleach-fixing solution containing the complex salt as a bleaching agent can attain some desirable objects when bleaching or bleach-fixing a low-speed silver halide color photographic light-sensitive material containing, for example, a silver chlorobromide emulsion as a major component. However, such a solution fails to fully remove silver due to insufficient bleaching power or requires a long time to bleach when processing a high-speed, spectrally sensitized silver halide color photographic light-sensitive material containing a silver chlorobromoiodide emulsion or silver bromoiodide emulsion as a major component, particularly color reversal light-sensitive materials for photographic use or color negative light-sensitive materials for photographic use comprising an emulsion containing larger amounts of silver.
Other known bleaching agents than ferric ion complex salts include persulfates. Persulfates are usually used in a bleaching solution together with a chloride. However, such a persulfate-containing bleaching solution has less bleaching power than ferric ion complex salts, thus requiring a substantially long period of time for bleaching.
As described above, bleaching agents which do not cause environmental pollution or corrode vessels and apparatuses have only a weak bleaching power. Hence, there has been a need to enhance the bleaching power of a bleaching or bleach-fixing solution containing a bleaching agent with a weak bleaching power, particularly a ferric ion complex salt or a persulfate.
In order to raise the bleaching power of a bleaching or bleach-fixing solution containing a ferric ion complex salt such as iron (III) ethylenediaminetetraacetate as a bleaching agent, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents include thiourea derivatives as described in Japanese Patent Publication No. 8506/70, U.S. Pat. No. 3,706,561, etc., selenourea derivatives as described in Japanese Patent Application (OPI) No. 280/71, five-membered ring mercapto compounds as described in British Pat. No. 1,138,842, and thiourea derivatives, thiazole derivatives, and thiadiazole derivatives as described in Swiss Pat. No. 336,257. Further, 5-mercaptotetrazoles as silver removal accelerating agents employed in a bleach-fixing solution are described in British Pat. No. 1,138,842. However, these compounds have a weak silver removal accelerating power and, therefore, have insufficient bleach accelerating effects, particularly on high-speed photographic light-sensitive materials. Thus, many of these bleach accelerating agents do not show a satisfactory bleach accelerating effect, or some of them lack stability in the processing solution although they have a good bleach accelerating effect. Therefore, they provide a processing solution having only a short effective life or which cannot be stored for a long time.